Milo g



. (No Model.)

- M. G. KELLOGG. MULTIPLE SWITGHBOARD.

i Patented 00's.. 26, 1897.

j Lime [6t FFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGG SWVITOIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,365, dated October 26, 1897'.

Application filed July 26, 1890. Serial No. 360,074. (No model.)

To all whom it may concern.-

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Multiple Switchboards for Telephone-Exchanges, of which the following is a full, clear, concise, and exact description, reference being bad to the accompanying drawings, forming a part of this specification.

My invention relates more especially to a telephone-exchange system in which the lines are single-circuit lines grounded at their outerends and normally grounded at the central office; and it consists in a system of testing thelines to determine whether they are in use.

In the drawings illustrating my invention, Figures 1 and 1 represent sections of two multiple switchboards of the exchange to which the same lines are connected. Fig. 2 shows a diagram of the boards, with the main-line apparatus and connections necessary to illustrate my invention. Fig. 3 shows a diagram of an operators cord system to be used in connection with the boards. Fig. 4 shows an operators test system to be used at the boards. Fig. 5 shows a subscribers-station apparatus.

In Fig. 2, A is a sectional View of the switchboard shown in Fig. 1, and A is a sectional view of the switchboard shown in Fig. 1", each as indicated by the line d e.

I place as many boards in the central office as are found necessary or desirable in order to properly operate the exchange. On each board is a spring-jack or other suitable switch for each line. Each switch has a contactspring which normally connects with an insulated contact-piece and is adapted to receive a loop-plug and, when a plug is inserted, to disconnect the spring from the c0ntact-piece and connect the two contactpieces of the plug with the spring and said insulated contact'piece, respectively. The switch is also adapted to receive a single-contact switchplug and, when a plug is inserted, to disconnect the spring from the contact-piece and connect the spring with the contact-piece of the plug. In the construction of the switches as shown and as will hereinafter be described I prefer to have a contact-point electrically connected with the contact-piece and on which the spring normally bears, as there is less chance of poor connection when the spring bears on a point than when it bears on a surface adapted to be brought into connection with the plug-contacts.

In Fig. 2, g g represent the springs of the different switches, h h the contact-points on which the springs normally bear, and j j the contact-pieces of the switches connected with the points it h. Z Z are the switch-holes. a b are the rubber strips on which the metal parts of the switches are mounted, as shown, and through the fronts of which are the switch-holes Z Z. The contact-piecesjj are so placed along one of the surfaces of the plugholes as readily to form connection with one of the contact-pieces of the loop-plugs. The holes H are adapted to receive the switchplugs shown in Fig. 3 and marked D D, and when a plug is inserted into a switch it raises the spring g from the contact-point h and the spring g and contact-piece of the plug are in contact. These holes are also adapted to receive the loop-plug shown in Fig. 4, and when a plug is inserted into a hole it raises the spring of the switch from the contactpoint h and the spring g and the contactpiece j of the switch are in contact with the two contact-pieces of the plug, respectively.

W and X are calling-annunciators, one for each of the lines shown.

lwo lines are shown in the drawings, one marked line No. 1 and the other line No. 2. These lines are ordinary single-circuit lines grounded at their, outer ends. Each line passes successively through the pairs of contacts of its switches on the several boards, passing in each case to the spring first.

the common ground wire or connection of the lines. The circuit of each line shown may thus be traced in Fig. 2.

In the operators cord system shown in Fig. 3, D D are the switch-plugs of a pair of It then passes through its line-annunciator to in Fig. 5, 1 is the telephone-switch.

vices may be used to bring the contact-pieces of the plugs into contact with the piece 0 and secure a good connection. These plugs are adapted to be inserted into any of the switches at their board, and when a plug is inserted it operates the switch, as above described. The plugs should be inserted so that the contact-piece m is in contact with the spring g. The connections of the lines might have been reversed, so that the lines pass first to the contact-piece j of each of their switches, and in that case the plugs should be inserted in such a position that their contact-pieces form connection with the pieces j of the switches. Y is the looping-in switch for the pair of cords shown. Kis the callingkey, and '1) is a clearing-out annunciator. tis the operators telephone, and B is her calling generator or battery. The circuits are substantially as shown.

The operation of. the system in connection with-the switchboards will be apparent to those skilled in the art. It will readily be apparentthat when a line is switched by the insertion of a plug into its switch the line is disconnected from its normal ground-wire at the central office and is connected into a circuit with the pair of-cords. cords is shown, but the connection of such other pairs,with their accompanying apparatus as the operator may need,will be apparent to those skilled in theart. To each pair of cords, with its plugs, belong a loopingin. switch, aclearing-out annunciator, and a call in g-key. One telephone and one calling-generat or will answerfor her system of cords.

In the operators test system shown in Fig. i

4, T is loop test-plug adapted to be inserted into any of the switches and when inserted to operate them, as heretofore described. B is a test-battery, and S is a test receiving instrument. battery are connected in a loop which terminates in the two contact-pieces of the plug. Each operator has one cord system and one test system,and they are conveniently mounted and arranged for her work. v

In the subscribers-station apparatus shown I 2 is the calling-generator. bell. 4.- is the subscribers telephone. 5 is the secondary, and 6 is the primary, of the induction-coil. 7 is the transmitter.

10 is a resistance-coil of suitable resistance to operate as hereinafter described. These parts i Only one pair of The instrument and the contact-pieces of the plug.

3 is the signal-receiving V V Sisthe transmitter-battery. 9 is a condenser, and

batteries should be so constructed and ad justed to each other and the circuits that the instrument will sound or respond when it and the battery are looped into the'closed circuit of any single line and the subscribers telephone is not off its switch for use, but willnot respond if the circuit is open at any point, or

if the subscribers telephone is oif its switch and the additional resistance at the subscribers station is included in the circuit, or the line is switched with another line and thereby has its test-circuit open, as will hereinafter be indicated, or the resistance of two lines isincluded in circuit with the instrument and battery. This adjustment can be regulated as required by the addition of artificial resistances in the circuits. This construction and adjustment dependson the fact that an electromagnet may be readily made so as to operate when a battery and a certain resistance are in circuit with it and not to operate when the resistance is considerably larger. This operation can be obtained in different ways,

dependent on the style of the electromagnet,

the number of convolutions of its coil, the size of the battery, and the adjustment of the retractile spring. These parts should be such that the electromagnet will be actuated when the test system is looped into the simple circuit of any line of the exchange, but willnot she places her test-plug into the switch of the line, and by so doing disconnects the points 9 and h of the switch and connects them with line is not switched at any board and the subscribers telephone is on its switch, the test receiving instrument will sound orrespond, indicating that the line is free to be switched to, for in that case the test receiving instrument and battery are looped into a closed circuit of the line which extends from the subscribers. ground through his station apparatus and line and through the normally closed contacts of the line-switches at the other boards and to ground at the central office, and the resistance of the circuit is so small thatsufficient current from the battery will pass through the magnet of the test receiving instrument to cause the force of the retractile spring of its armature to be overcome. and the armature to move and strike telephone from the switch for use, the in-.

IIO

If, then, the

strument will not sound, as the additional resistance in the circuit will prevent it from doing so. In that case the additional resistance in the line-circuit causedby the switching of the telephone for use isso great that although current from the battery passes through the instrument and continually causes the armature to be attracted the current is not strong enough to overcome the adjusted retractile force of the armature-spring and the arma ture will not move to strike the gong. If,again, the line is switched at some board and the test is madein the cut-off portion of the line that is, that portion which is between the switch used for switching and the office groundthe instrument will not sound, because the testcircuit is open at the pair of contact-points of the switch used for switching. In that case no current at all is passing through the test receiving instrument and no attraction is produced in its magnet. If, again, the line is switched at any board with another line and the test is made in some switch between the one used for switching and the subscribers station, the instrument will not sound on account of the resistance of the two lines being in the circuit in which the test receiving i11- strument and battery are included. If in that case either or both the subscribers telephones are switched for use, the resistance of their station apparatus will be so greatthat enough current will not be allowed to pass through the test receiving instrument to cause its armature to move. The instruments and battery may be also so adjusted to the linecircuits and apparatus that in that case the armature will not be sufficiently attracted to move even if both subscribers telephones are on their switches.

Then, as described above, the test receiving instrument and battery are placed for testing in closed circuit with the subscribers condenser and resistance-coil in multiple or parallel circuit, continuous current from the battery will pass through the instrument, attracting its armature and tending to move it. On account of the increased resistance sufficient current does not, however, then pass to overcome the retractile force of the adjustment-spring and the armature will not be moved. \Vhen, however, the line is not switched and the subscribers telephone is not switched and the test instrument and battery are included in its circuit, the resistance of the circuit is so small in relation to the strength of the battery and the character and adjustment of the test receiving instrument that: suilicient current will pass through the instrument to cause its armature to move and the sound to be given. This system therefore depends on a marginal adjustment of these parts to each other and to the resistances tosecure the sound of the test receiv ing instrument when neither the line nor the subscribers telephone is switched for use and to insure that it does not sound when either. areswitched for use. The resistance-coil furbeing made.

nishes the additional resistance required in the circuit when the subscribers telephone is switched for use to provide for the operation of the test system as described, while the condenser provides an easy circuit or path for the passage of the telephone-currents. The resistance-coil, moreover, provides an all-metallic circuit through the subscribers line for the passage of the clearing-out currents, especially when one subscriber sends the clearingfout signal while the other subscriber has not yet placed his telephone on his switch, as may often be the case. With the forms of apparatus used in telephone-exchanges the clearing-out signals will be readily operated over the resistances necessary to produce the marginal adjustment of the test system which has been described.

When a test of line is made and the test receiving instrument sounds, the operator knows that neither the line is switched for use nor the subscribers telephone is switched for use, and when the instrument does not sound she knows that either the subscribers telephone is switched for use or the line is switched for use and she will not connect the line with any other line. By this system a subscribers line is reserved to himself fromv the time his telephone or the line is switched for use.

In multiple-switchboard systems an opera.

tor to whom certain lines are assigned to answer frequently receives several calls at practically the same moment, and it may require some time before she can switch to a certain line and answer its call. In systems in which the test depends only on the line being switched at some board another operator may in the meantime test the line and, findingit to test free, may switch it with another line and cause annoyance and confusion to the subscriber. This cannot occur in this system of testing, because as soon as the subscriber takes his telephone from its switch the line will test busy, whether or not it is switched at the central office. Again, in systems of testing which depend only on the subscribers telephone being on or off its switch confusion frequently arises from the fact that a subscriber places his telephone on its switch when he is through conversation without sending in a clearing-out signal and his line tests free and is connectedto when it is already switched with another line. Lines in this condition are technically called tied up. This, again, cannot occur in this system because the line will test busy until it is disconnected at the central office, whether or not the subscribers telephone is on its switch. The system therefore combines the advantages and obviates the disadvantages of the two general systems of testing outlined above.

The annunciators will be so related to the testbatteries that they will not be made to indicate when closed with each other on atest They may for this purpose be polarized annunciators so connected with reference to the batteries that the batteries will not operate them or they may not be of a sufficiently sensitive construction to be operated by the test-batteries.

I claim as my invention and desire to secure by Letters Patent 1. In a multiple telephone-exchange system, telephone-lines each normally passing successively through pairs of switch contactpoints, one pair on each of several boards, each pair normally closed but open while the line is switched at their board, in combination with switching devices at each board to disconnect the pair of contact-points at the board and switch the line with another line for conversation, a condenser and a resistance-coil in multiple or parallel circuit at the subscribers station and a switch with contact-points to switch them 'into circuit while the subscribers telephone is switched for use and out of circuit with the line while the telephone is not thus switched, and a loop testplug in the two contact-pieces of which terminate the two sides of a loop which contains a test receiving instrument and battery, said plug being adapted to be inserted into the switch at the board where it is located and when inserted to disconnect the pair of contact-points of the switch and connect them .with the contact-pieces of the plug, said test receiving instrument being adjusted to the battery and resistances to the extent that the instrument will sound when it is'looped into the normal closed circuit of the line when the telephone is not switched for use, but will not sound when it is in an open circuit or is looped into circuit with a line which is switched for conversation into circuit with another line or-has its subscribers telephone switched for use, and the additional resistance is thereby switched into circuit with the line, whereby a condenser-path is provided at the subscribers station for the telephonecurrents, and the differentiation of the various multiple-test signals is obtained by a marginal adjustment of the apparatus, substantially as set forth.

2. In a multiple telephone-exchange system, telephone-lines each grounded at its outer end and passing normally successively through pairs of switch contact-points, one pair on each of several boards, each pair normally closed but open while the line is switched at their board, and thence to ground, in combination withswitching devices at each board to disconnect the pair of contact-points at each board and switch the line with another line for conversation, a condenser and a resistance-coil in multiple or parallel circuit at the subscribers station, and a switching device to switch said condenser and coil.

into the circuit of the line while the subscribers telephone is switched for use and out of the circuit while the telephone is not thus switched, and a loop test-plug at one of the boards in the two contact-pieces of which terminate the two sides of a loop which contains a test receiving instrument and battery, said plug being adapted to be inserted into the switch at the board where it is located and when inserted to separate the pair of contact-points of the switch and connect them with the contact-pieces of the plug, the resistance in the circuit of the line at the subscribers station when his telephone is switched for use being then as much increased, and said test receiving instrument being adj usted to the battery and resistances to the eX- tent that the instrument will sound when it is looped into the normal closed circuit of the line, when the telephone is not switched for use, but will not sound when it is in an open circuit or is looped into circuit with the line when it is switched for conversation into circuit with another line or has its subscribers telephone switched for use, and the additional resistance is thereby switched into circuit with the line, whereby a condenserpath is provided at the subscribers station for the telephone-currents, and the differ- V entiation of the various multiple-test signals is obtained by a marginal adjustment of the apparatus.

3. In a multiple telephone exchange system, telephone-lines each normally on closed circuit and passing successively through pairs of switch contact-points, one pair on each of several boards, each pair normally closed but open while the line is switched at their board, in combination with switching devices at each board to disconnect the pair of contact-points at the board and switch the line for conversation with another line, a condenser and a resistance-coil in multiple or parallel circuit at the subscribers station and a switch wit-l1 contact-points to switch said condenser and resistance-coil into the circuit of the line while the subscribers telephone is switched for use and out of the circuit while the telephone is not thus switched, and a loop testplug at one of the boards in the two contactpieces of which terminate the two sides of a loop which contains a test receiving instrument and battery, said plug being adapted to be inserted into the switch at the board where it is located and when inserted to disconnect said contact-points of the switch and connect them with the contact-pieces of the plug, the resistance in the circuit of the line at the subscribers station beingso much increased when his telephone is switched for use and said test receiving instrument being adjusted to the battery and resistances to the extent that the instrument sounds when looped into the normal closed circuit of the provided at the subscribers station for the telephone-currents and the differentiation of the various multiple-test signals is obtained by a marginal adjustment of the apparatus.

4. In a multiple telephone-exchange system, telephone-lines each normally on closed circuit and passing successively through pairs of switch contact-points, one pair on each of several boards, each pair normally closed but open while the line is switched at their board, in combination with switching devices at each board to disconnect the pair of contact-points at the board and switch the line with another line for conversation, a condenser and a resistance-coil in multiple or parallel circuit at the subscribers station and a switch with contact-points which switch said condenser and coil in multiple or parallel circuit into the circuit of the line while the subscribers telephone is switched for use, and out of circuit while the telephone is not thus switched, a loop test-plug at one of the boards in the two contact-pieces of which terminate the two sides of a loop which contains a test receiving instrument, said plug being adapted to be inserted into the switch at the board where it is located and when inserted to disconnect the contact-points of the switch and connect them with the c0ntaet-pieces of the plug, and battery in the test-circuit established on testing, the resistance in the circuit of the line at the subscribers station being so much increased when his telephone is switched for use, and said test receiving instru nent being adjusted to the battery and resistances to the extent that the instrument sounds when looped into the normal closed circuit of the line when the telephone is not switched for use, but will not sound when in an open circuit or looped with a line when the line is switched for conversation into circuit with another line or has its subscribers telephone thereby switched for use, and the additional resistance is switched into circuit with the line, whereby a condenser-path is provided at the subscribers station for the telephone-currents and the difierentiation of the various multiple-test signals is obtained by a marginal adjustment of the apparatus. 7 5. In a multiple telephone-exchange system, telephone-lines each normally on closed circuit and passing through a series of pairs of contacts at the several boards, one pair at each of the boards, in combination with a test receiving instrument and battery at each board and a testing device connected therewith, adapted at the will of the operator to open said contacts at the board, and loop said instrument and battery into the circuit of the line when thus normally 011 closed circuit, apparatus at the subscribers station normally in the direct circuit of the line, other apparatus at the subscribers station of greater resistance and of metallic continuity to battery-currents normally out of the direct circuit of the line, switching devices and circuit connections at the subscribers station to include the apparatus of greater resistance in the direct circuit of the line while his tele phone is switched for use, and a condenser in multiple or parallel circuit to said apparatus of greater resistance, each test receiving instrument being adjusted to the battery and the resistances to the extent that when thus looped into the normally-unswitched circuit of the unswitched line and the subscribers telephone is not switched for use, the instrument will sound, but when the telephone is switched for use and the additional resistance is included in the circuit the instrument will not sound, whereby a condenser-path at the subscribers station is provided for the telephone-currents and by the differentiation of the multiple-test signals obtained by a marginal adjustment of the apparatus, the line is prevented from being switched to at either of the boards from the time the subscriber switches his telephone for use.

(5. In a multiple telephone-exchange system, telephone-lines each normally on closed circuit and passing through a series of pairs of contacts at the several boards, one pair at each of the boards, in combination with a test re ceiving instrument at each board, and a testing device connected therewith, adapted at the will of the operator to open said contacts at the board and loop said instrument into the circuit of the line when thus normally on closed circuit, apparatus at the subscribers station normally in the direct circuit of the line, other apparatus at the subscribers station of greater resistance and of metallic con tinuity to battery-currents normally out of the direct circuit of the line, switching devices and circuit connections at the subscribers station to include the apparatus of greater resistance in the direct circuit of the line, while his telephone is switched for use, and a battery in any closed circuit thus established on testing, and a condenser in multiple or parallel circuit to said apparatus of greater resistance, each test receiving instrument beingadjusted to thebattery and the resistances to the extent that when thus looped into the normally unswitched circuit of the unswitched line and the subscribers telephone is not switched for use the instrument will sound, but when the telephone is switched for use and the additional resistance is included in the circuit the instrument will not sound, whereby a condenser-path at the sub scribers station is provided for the telephonecurrents and by the differentiation of the multiple-test signals obtained by a marginal adjustment of the apparatus, the line is prevented t'rom being switched to at either of the boards from the time the subscriber switches his telephone for use.

7. In a multiple telephone-exchange system, telephone-lines each normally on closed circuit, and passing through a series of pairs of contacts at the several boards, one pair at each of the boards, in combination with switching apparatus at each board to at the will of the operator connect any two lines into a closed circuit for conversation, a clearing-out-annunciator circuit with the two lines when thus connected, a test receiving instrument and battery at each board and a testing device connected therewith, adapted at the will of the operator to open said contacts at the board and loop said instrument and battery into the normal line-circuit, apparatus at the subscribers station of metallic continuity normally in the direct circuit of the line, other apparatus at the subscribers station, of greater resistance and also of metallic continuity normally out of the direct circuit of the line, switching devices and circuit connections at the subscribers station to include the apparatus of greater resistance in the direct circuit of his line, while his telephone is switched for use, and a condenser in multiple or parallel circuit to said apparatus of greater resistance, each test receiving instrument being adjusted to the battery and the resistances to the extent that Whenthe apparatus the line is prevented from being switched to at either of the boards from the time the subscriber switches his telephone for use.

8. In a multiple telephone-exchange system, telephone-lines each normally on closed circuit, and passing through a series of pairs of contacts at the several boards, one pair at each of the boards, in combination with switching apparatus at each board to at the will of the operator connect any two lines into a closed circuit for conversation, aclearin g-out-annunciator circuit with the two lines when thus connected, a test receiving instrument at each board, and a testing device connected therewith, adapted at the will of the operator to open said contacts at the board and loop said instrument into the normal line-circuit, apparatus at the subscribers station of metallic continuity normally in the direct circuit of the line, other apparatus at the subscribers station of greater resistance and also of metallic continuity normally out of the direct circuit of the line, switching devices and circuit connections at the subscribers station to include the apparatus of greater resistance in the direct circuit of his line, while his telephone is switched for use, and a battery in any closed circuit thus established on testing, and a condenser in multiple or parallel circuit to said apparatus of greater resistance, each test receivinginstriunent being adjusted to the battery and the resistances to the extent that when thus looped into the circuit of an unswitched line and the subscribers telephone is not switched for use, the instrument will sound but when the telephone is switched for use and the additional resistance is included in the circuit the instrument will not sound, whereby a condenser-path at the subscribers station is obtained for the telephone-currents, a circuit of metallic continuity is obtained for the clearing-out current, and by the differentiation of the multiple-test signals obtained by a marginal adjustment of the apparatus the line is prevented from being switched to at either of the boards from the time the subscriber switches his telephone for use.

In witness whereof I hereunto subscribe my name this 23d day of June, 1890.

. MILO G. KELLOGG. Witnesses:

EMIL ABENHEIM,

(J. STRIcH-CHAPELL. 

